There is usually an interface chip which sits between the actual bus wires and the device that logically plugs into it, such as memory or the CPU. This interface chip may do useful things like match voltage or amplify the signals so that they will be strong enough to assert logic 1 or 0 on the bus wires. Internal buses seldom have these problems since they are always connected and the chip designer knows how much current is passing through at any point and can match things up.

External buses, such as system buses, often connect heterogeneous equipment, often from different vendors, and it must all work together. A new trend, plug 'n' play as it is called, has emerged with Windows 95 (although a form of it was present in some earlier computers such as the Macintosh). In this system, no special addressing must be done in order to get the other devices on the bus to recognize the unit just plugged in. This is done automatically by the devices through sending and receiving signals to each other. In the (recent) past, you would have had to have changed configuration files when you added new hardware to your IBM PC or clone.